1. Field of the Invention
The present invention relates to a rotary polishing tool which is driven by an electric motor for polishing a workpiece.
2. Description of the Prior Art
Such rotary polishing tools conventionally used include one comprising a disk-shaped polishing portion corresponding to a workpiece and a disk-shaped substrate made of resin for supporting the polishing portion with the polishing portion being bonded thereto. The polishing work using such a rotary polishing tool is performed by mounting this tool on a driving shaft of an electric motor and rotating the same to press the above polishing portion against the workpiece.
Meanwhile, during the above described work, the tool is rotated at high peripheral speed of, for example, a maximum of approximately 80 m/s. Consequently, a substantially large centrifugal force is developed in this tool. In addition, a large reaction force is applied to this tool from the workpiece. Accordingly, it is particularly desired that the above substrate has sufficient strength.
Therefore, it is considered that the above substrate is made of metal to improve the strength thereof. If this substrate is merely a metal plate, however, such problems arise that the tool becomes heavy and the centrifugal force becomes the larger.
Furthermore, if the above metal plate is merely flat, there is a possibility that a part of the polishing portion is stripped off from the substrate by an impact force applied to the polishing portion from the workpiece during the work, resulting in insufficient strength to support the polishing portion by the substrate.